Colors are widely used in multimedia content to convey visual information. However, around 5%-8% of men and 0.8% of women have certain kinds of colorblindness, i.e., have difficulty in discriminating certain color combinations and color differences.
Colors are perceived by a human with the cones of the eyes absorbing photons and sending electrical signals to the brain. According to their peak sensitivity, these cones can be categorized into Long (L), Middle (M) and Short (S), which absorb long wavelengths, medium wavelengths and short wavelengths, respectively. Consequently, light is perceived as three members: (l, m, s) where l, m, and s represent the amount of photons absorbed by L-, M- and S-cones, respectively. More formally, color stimulus (Si) for a light can be computed as the integration over the wavelengths λ:Si=∫φ(λ)li(λ)dλ,i=L,M,S;  (1)where φ stands for power spectral density of the light, lL, lM, and lS indicate L-, M- and S-cones.
Colorblindness, formally known as color vision deficiency, is caused by the deficiency or lack of certain types of cones. Those who have only two types of cones are referred to as dichromats. There are three types of dichromats: namely protanopes, deuteranopes, and tritanopes, which indicate the lack of L-cones, M-cones and S-cones, respectively. Protanopes and deuteranopes have difficulty in discriminating red from green, whereas tritanopes have difficulty in discriminating blue from yellow. Most dichromats belong to either the protanopia or deuteranopia types.